A helix hearing instrument comprises a receiver inserted into the ear canal and an electronics assembly, comprising a microphone, amplifier, and battery, which typically resides in the helix of the user's ear. The helix hearing instrument has a capability limited in part by the size of the electronics assembly and the space available for batteries and the instrument's components. Additional capabilities or functions for the instrument and longer battery life may be offered in an accessory module that rides behind the ear in the same fashion as a behind-the-ear hearing instrument.